An internal combustion engine is used as a drive for motor vehicles. Within the context of the present disclosure, the expression “internal combustion engine” encompasses Otto-cycle engines and diesel engines but also hybrid internal combustion engines, which utilize a hybrid combustion process, and hybrid drives which comprise not only the internal combustion engine but also an electric machine which is connectable in terms of drive to the internal combustion engine and which receives power from the internal combustion engine or which, as a switchable auxiliary drive, outputs power in addition.
Internal combustion engines have a cylinder block and at least one cylinder head which can be or are connected to one another in order to form the individual cylinders, that is to say combustion chambers. The individual components are discussed briefly below.
To hold the pistons or the cylinder liners, the cylinder block has a corresponding number of cylinder bores. The piston of each cylinder of an internal combustion engine is guided in an axially movable manner in a cylinder liner and, together with the cylinder liner and the cylinder head, delimits the combustion chamber of a cylinder. Here, the piston crown forms a part of the combustion chamber inner wall, and, together with the piston rings, seals off the combustion chamber with respect to the cylinder block or the crankcase, such that no combustion gases or no combustion air pass(es) into the crankcase, and no oil passes into the combustion chamber.
The pistons serve to transmit the gas forces generated by combustion to the crankshaft. For this purpose, each piston is articulatedly connected by means of a piston pin to a connecting rod, which in turn is movably mounted on the crankshaft.
The crankshaft is mounted in the crankcase and absorbs the connecting rod forces, which are composed of the gas forces as a result of the fuel combustion in the combustion chamber and the mass forces as a result of the non-uniform movement of the engine parts. Here, the oscillating stroke movement of the pistons is transformed into a rotating rotational movement of the crankshaft. The crankshaft transmits the torque to the drivetrain. A part of the energy transmitted to the crankshaft is used for driving auxiliary units such as the oil pump and the alternator, or serves for driving the camshaft and therefore for actuating the valve drive.
Generally, and within the context of the present disclosure, the upper crankcase half is formed by the cylinder block. The crankcase is completed by the lower crankcase half which can be mounted on the upper crankcase half and which serves as an oil pan. Here, to hold the oil pan, that is to say the lower crankcase half, the upper crankcase half has a flange surface. In general, to seal off the oil pan or the crankcase with respect to the environment, a seal is provided in or on the flange surface. The connection is often provided by means of screws.
To hold and mount the crankshaft, at least two bearings are provided in the crankcase, which bearings are generally of two-part design and comprise in each case one bearing saddle and one bearing cover which can be connected to the bearing saddle. The crankshaft is mounted in the region of the crankshaft journals which are arranged spaced apart from one another along the crankshaft axis and are generally formed as thickened shaft shoulders. Here, bearing covers and bearing saddles may be formed as separate components or in one piece with the crankcase, that is to say with the crankcase halves. Bearing shells may be arranged as intermediate elements between the crankshaft and the bearings.
In the assembled state, each bearing saddle is connected to the corresponding bearing cover. In each case one bearing saddle and one bearing cover—if appropriate in interaction with bearing shells as intermediate elements—form a bore for holding a crankshaft journal. The bores are conventionally supplied with engine oil, that is to say lubricating oil, such that a load-bearing lubricating film is ideally formed between the inner surface of each bore and the associated crankshaft journal as the crankshaft rotates—similarly to a plain bearing. Alternatively, a bearing may also be formed in one piece, for example in the case of a composite crankshaft.
To supply the crankshaft bearings with oil, a pump for delivering engine oil to the at least two crankshaft bearings is provided, with the pump supplying engine oil via a supply line to a main oil gallery, from which ducts lead to the at least two bearings.
To form the so-called main oil gallery, a main supply duct is often provided which is aligned along the longitudinal axis of the crankshaft. The main supply duct may be arranged above or below the crankshaft in the crankcase or else at the same level, in particular may be integrated into the crankshaft.
The oil-conducting lines of the oil circuit lead through the cylinder block and, if appropriate, through the cylinder head, may also emerge from and re-enter the block and/or head several times, and may, alternatively or in addition to the crankshaft bearings, supply oil to further bearings, for example the bearings of a camshaft, which is generally mounted in a two-part so-called camshaft receptacle. The statements already made above with regard to the crankshaft bearing arrangement apply analogously. The camshaft receptacle must normally also be supplied with lubricating oil, for which purpose a supply line must be provided which, in the case of overhead camshafts, extends into the cylinder head and, according to the prior art, is commonly connected to the main oil gallery and leads through the cylinder block.
Further bearings may for example be the bearings of a connecting rod or the bearings of a balancing shaft which may be provided if appropriate.
The friction in the bearings to be supplied with oil, for example, the bearings of the crankshaft, is dependent significantly on the viscosity and therefore the temperature of the oil which is provided, and said friction contributes to the fuel consumption of the internal combustion engine.
It is fundamentally sought to minimize fuel consumption. In addition to improved, that is to say more effective, combustion, the reduction of friction losses is also in the foreground of the efforts being made. Moreover, a reduced fuel consumption also contributes to a reduction in pollutant emissions.
With regard to reducing friction losses, rapid heating of the engine oil and fast heating-up of the internal combustion engine, in particular after a cold start, is expedient. Fast heating of the engine oil during the warm-up phase of the internal combustion engine ensures a correspondingly fast decrease in viscosity, and therefore a reduction in friction and friction losses, in particular in the bearings which are supplied with oil.
The prior art discloses concepts in which the oil is actively heated by means of a heating device after a cold start. The heating device itself however in turn consumes fuel and thus contributes, in a counterproductive manner, to increased fuel consumption. In other concepts, the engine oil which is heated during operation is stored in an insulated container, such that already-heated oil is available in the event of a re-start of the internal combustion engine. A disadvantage of the latter approach is that the oil which is heated during operation cannot be kept at a high temperature indefinitely, for which reason re-heating of the oil is usually necessary during the warm-up phase of the internal combustion engine.
With regard to the reduction of friction losses, it must be taken into consideration that the oil additionally has heat extracted from it as it flows through the crankcase, which immediately after a cold start has not yet warmed up, such that the heating of the oil cannot be expedient on its own without further measures.
Even if, after a cold start, the oil is heated by means of a heating device or is delivered, in the already-heated state, out of an insulated container, the hot oil cools again on the path to the bearings in the oil-conducting lines of the oil circuit owing to the fact that the engine structure has not yet heated up, such that oil available or made available at the bearings is not noticeably warmer.